Demonstrate your ability to teach a concept to a student of interviewer's choice for the level class you will be teaching (algebra, calculus, C++ Data structures, etc.) through pretending. They give you a question, pretend to be a student who needs help, just simply explain how to solve the problem as if the interviewer knows absolutely nothing. They ask a few questions to make sure you know the subject you're applying for, so make sure you know it. It's okay if you don't know the answer, just walk through it and explain everything the best you can, they're measuring you more on your ability to be kind, informative, helpful, and passionate (not boring).